1. Field of the Invention
The present invention relates to a color curve control circuit and method. Specifically, this invention easily adjusts the colors as desired by the user, on the screen of a monitor using color gain and cutoff signals corresponding to the color temperature.
2. Discussion of Related Art
Red does not indicate just one color. There are many variant colors from a red similar to orange to purplish red. There are also variant colors such as yellowish white and bluish white in white resulting from mixture red (R), green (G), and blue (B). Therefore, it is necessary to define the desirable three primary colors of light, R, G, and B, and standard white. The standard colors are employed by Commission International de L'Eclairage (CIE), and represented with R, G, B, and white points of light.
CIE defines the three primary colors according to wavelengths, thus light of 700 nm (nanometers) is defined as R, the light of 546 nm is defined as G, and the light of 435 nm is defined as B. CIE uses color matching where mix ratios of the three primary colors are calculated using a color matching measurement device to obtain various colors, thus colors are created by mixing the three colors according to calculated ratios.
Since human eyes sense colors differently and individually, and since they are most sensitive to the light near 550 nm, there are large perceived differences between R, G, B when the intensities of the three primary colors are represented by the absolute lumen or watt values. In color matching, a standard white is defined as the amount of R, G, and B which is necessary to match the standard white, and the amount of white, that is R+G+B, is set to 1. The amounts of R, G, and B is represented with a ratio to the white. For example, a color of 600 nm is made by mixing 0.34 of R, which is necessary to make the standard white, with 0.07 of G, which is also necessary to make the standard white. Such a mixing method is called a tristimulus value. An example is given below to demonstrate a conventional color mix method using this tristimulus value.
People react differently to colors. The same color can be perceived differently by different people. Therefore, colors are very important to a user who uses a monitor while working.
For example, when G and B are reduced from the value of a 9300° K (Kelvin) white, the R value becomes relatively large and reddish colors are displayed. The user can utilize different standard white value in the manner that he/  or she stores different standard white values in memory and selects from them. For this, monitor manufacturers provide several limited colors, or values, which are most frequently utilized by the users. High quality monitors are designed so that the uses can adjust the colors, but inaccurate color values are utilized because they must select them depending on their own eyes.
The values supplied to users are abstract virtual color values, not the color values which appear actual color characteristics. When some software applications requiring more precise colors need a white value for the monitor, the users can only utilize the colors which are set during manufacture because they cannot know the white value of the monitor. Therefore, it is difficult for the users to adjust colors to particular values, and it takes much time. It is also a problem that the users cannot utilize a color adjustment function even though the monitor has this function.